Various domestic network standards are available for the networking of devices in the domestic field. One consortium of companies, in particular the companies in the computer industry, led by Microsoft, have started an initiative for the specification of network control software, based on the existing Internet Protocol (IP). This network system has become known by the abbreviation UPnP (Universal Plug and Play). The UPnP system is based on a series of standardized network protocols and data formats and is used for controlling devices from different manufacturers (including typical devices from the computer industry such as PCs, routers, printers, scanners, as well as domestic entertainment electronic devices as well as domestic devices in the field of white goods and building control systems). The devices are networked via an IP-based network, with or without central monitoring by a “residential gateway”. In this case, the network system is in the form of a plug and play system, that is to say the network is configured without any interaction with the user. A control point device, corresponding to a control point, can autonomously find the devices in the network. All types of medium which support IP communication can be used as physical transmission media, that is to say by way of example Ethernet, Firewire, radio transmission systems such as Bluetooth and WirelessLAN etc. Standardized technologies such as IP, UDP, corresponding to User Datagram Protocol, Multicast, TCP corresponding to Transmission Control Protocol, HTTP, corresponding to Hyper Text Transfer Protocol, XML, corresponding to Extended Mark up Language, SOAP, corresponding to Simple Object Access Protocol and SSDP, corresponding to Simple Service Discovery Protocol are used.
The UPnP specification describes how devices based on the UPnP standard are set up, and how they can be monitored. One of the basic ideas of this specification is that it is possible to operate any UPnP device via a standard web browser. For this purpose, every UPnP device has a web server on which the HTML pages for operation of the device (the so-called presentation pages) are stored.
In the UPnP network system, a confirmation process is carried out in which new stations in the network must log on, and disconnected stations must log off from the network. This is done by means of special messages in accordance with the SSDP protocol. The UPnP standard provides for the individual network stations to regularly notify their activity. This is done by means of an SSDP message, specifically “ssdp:alive”, which a network station must send at least every 1800 seconds. This corresponds to a minimum session duration of half an hour.
When the devices leave the network, they should also send a logging-off message of the “ssdp:byebye” type. When the logging-off message is sent, a control point device can use this to quickly confirm that a UPnP device has left the network. In addition, the control point device could also use the lack of any activity confirmation message after the defined repetition interval to identify that the corresponding network station has been switched to be inactive. In fact, it is possible for the devices to send an ssdp:byebye message when they are switched off and thus in principle are no longer in the network—even if they are still connected to it. However, if they are disconnected from the network by pulling out the cable, it is no longer possible for physical reasons to send the logging-off message that has been mentioned. Since the minimum time period to be observed is, however, rather long at half an hour, this can have unexpected reactions for the user. Particularly if a user wishes to use a device which has already been switched to be no longer active for some time, but the activity confirmation message has not yet been absent for the maximum permissible period, the network does not respond ideally. This is because, as soon as it accesses the supposedly existent device, it finds that it is no longer active and it will suddenly disappear from the user menu, which can confuse the user.